This application addresses broad challenge area (03): Validation and Specific Challenge Topic 03-AT-102: Antioxidant biomarkers. Development and validation of biomarkers of oxidative stress that could be used to assess the antioxidant effects of dietary supplements in vivo. Parkinson's Disease (PD) as well as other neurodegenerative diseases are associated with oxidative damage. In PD, there is an early reduction in reduced glutathione in the substantia nigra, as well as increases in markers of lipid, protein and DNA oxidation. A number of laboratories have reported increases in plasma and cerebrospinal fluid biomarkers of oxidative stress in PD. We recently found reduced uric acid and increased 8-hydroxy-2-deoxyguanosine (8-OHdG) in plasma of PD patients. We are presently carrying out a phase III clinical trial of the antioxidant nutritional supplement coenzyme Q10 (CoQ10) in PD. Six hundred newly diagnosed unmedicated PD subjects are being randomized to placebo, 1200mg of CoQ10 or 2400 mg of CoQ10 daily. Patients are assessed using the Unified Parkinson's Disease Rating Scale (UPDRS) every 3 months until they require dopaminergic therapy or they complete 16 months. We propose to measure several markers of oxidative damage at baseline, 1, 8 and 16 months of therapy. We will measure plasma levels of 8-OHdG, malondialdehyde, ascorbic acid, uric acid, oxidized and reduced CoQ10, and oxidized and reduced glutathione. All samples will be examined using metabolomic profiling using HPLC with coulometric array detection. This results in detection of up to 2000 small molecules, which are electrochemically active. The measurements of individual peaks will be correlated with those of established markers of oxidative damage such as 8-OHdG, malondialdehyde and the ratio of oxidized/reduced glutathione, to see if more sensitive and specific novel biomarkers of oxidative stress can be identified. The biomarkers will be correlated with clinical improvements in PD patients as assessed using UPDRS scores. These studies will establish the relative utility of existing biomarkers of oxidative damage, and may lead to the development of novel biomarkers, which will be useful in assessing the efficacy of the antioxidant effects of dietary supplements in vivo, and will help in assessing their effectiveness with respect to human health. As such, these studies may be useful in establishing the effectiveness of a large number of dietary interventions, which may impact human health. Public Health Relevance: This study proposes to identify biomarkers of oxidative stress to facilitate in vivo study of the antioxidant effects of the dietary supplement coenzyme Q10 (CoQ10). We intend to comprehensively evaluate a panel of established markers of oxidative damage and to utilize metabolic profiling to identify novel markers of oxidative stress. We will examine the relative sensitivity of these biomarkers in relationship to clinical efficacy of CoQ10 in a phase III clinical trial in Parkinson's Disease. The development of useful biomarkers to assess oxidative stress in relationship to human health, has the potential of having a major impact in the development of therapies to treat and prevent neurodegenerative diseases. These biomarkers may be useful in assessing therapeutic interventions in numerous other human illnesses in which oxidative stress plays an important role.